AVL Tree Deletion using Recursion

Question

Let x = the node to be deleted

How can I reassign the left or right pointer of x's parent to x's left or right sub tree during rotation without a parent pointer in node's struct declaration using recursion in an AVL Tree Implementation coded in C?

My Node's struct declaration:

typedef struct Node{
    int key;
    struct Node *left;
    struct Node *right;
    int height;
}node;

Currently, these are my rotation codes:

void rotateRight(node **n){

    node *lChild = (*n)->left;
    node *subtree = lChild->right;

    // Rotate Right
    lChild->right = *n;
    (*n)->left = subtree;
    *n = lChild;

    // Update Height
    lChild->right->height = max(getHeight(lChild->right->left), getHeight(lChild->right->right)) + 1;
    (*n)->height = max(getHeight((*n)->left), getHeight((*n)->right)) + 1;
}

void rotateLeft(node **n){

    node *rChild = (*n)->right;
    node *subtree = rChild->left;

    // Rotate Left
    rChild->left = *n;
    (*n)->right = subtree;
    *n = rChild;

    // Update Height
    rChild->left->height = max(getHeight(rChild->left->left), getHeight(rChild->left->right)) + 1;
    (*n)->height = max(getHeight((*n)->left), getHeight((*n)->right)) + 1;
}

When I execute these rotation codes, I lose some elements that should have not been deleted.

Answer 1

You can't. Either add a pointer to parent to your structure, or write your recursion in a way that passes node and parent on each level, so you can pass the parent as a second parameter to your rotate functions.